In many systems, in particular in the automotive field, very precise and reliable determination of a rotational direction and/or rotational speed, for example, for wheels or shafts, is required. For this purpose, the systems for determining the rotational direction and/or rotational speed analyze one sinusoidal and one cosinusoidal acceleration signal in the formx=cos φy=sin φ.
Angle φ is the instantaneous value of the (rotational) angle of the wheel or the shaft. The sensors are situated at different positions on the rim of the wheel or on the shaft or are sensitive in different directions. Both signals x and y normally have a phase shift of 90° in relation to one another.
Methods are known from the related art which monitor signals x and y and determine the rotational direction of the wheel or the shaft from the sequence of the minima and maxima of the two signals. For example, it is possible to monitor signal x and to detect the point in time at which signal x has the first zero crossing after a maximum. If signal y has a maximum at this point in time, the wheel or the shaft rotates in the positive direction of φ. If signal y has a minimum at this point in time, in contrast, the wheel or the shaft rotates in the negative direction of φ.
However, these methods have certain disadvantages. In general, the detected signals are subject to offsets, i.e., to a constant component, or have interference of another type, whereby the detection of the minima, maxima, and zero crossings, which is required during the entire monitoring time, proves to be problematic. Because of the long monitoring time, the analysis circuit used has increased power consumption, because it must be continuously powered. Furthermore, the above-mentioned methods only provide information about the rotational direction, but not additional information such as the rotational frequency, etc.
Therefore, the need exists for an improved method for efficient determination of the rotational direction and/or rotational speed of a rotatable body.
It is therefore the object of the present invention to provide a method for the efficient determination of the rotational direction and/or rotational speed of a rotatable body which avoids the above-mentioned disadvantages. This object is achieved by the subject matter of Claim 1.
A further object of the present invention is to provide a device for the efficient determination of the rotational direction and/or rotational speed of a rotatable body. This object is achieved by the subject matter of Claim 8.
Furthermore, the present invention has the object of providing a computer program which executes all steps of the method according to the present invention when it runs on a computing device. This object is achieved by the subject matter of Claim 9.
A computer program product having program code, which is stored on a machine-readable carrier, for performing the method according to the present invention when the program is executed on a computer or control unit is the subject matter of Claim 10.
Specific embodiments and refinements and supplementary methods are the subject matter of the embodiments and methods described herein.
The method according to the present invention for determining rotational direction and/or rotational speed ω of a rotatable body on the basis of a sine signal (y) and cosine signal (x), which is assignable to the rotational direction and/or rotational speed of the rotatable body and are output by a sensor, has at least one of the following steps: recording a sine signal (y0) and cosine signal (x0), which is assignable to the rotational direction and/or rotational speed, at a point in time t0; determining a phase value of φ0 from sine signal (y0) and cosine signal (x0); recording sine signals (yi) and cosine signals (xi), which is assignable to the rotational direction and/or rotational speed, at points in time ti; determining phase values φi from the corresponding sine signals (yi) and cosine signals (xi); calculating phase differences Δφi from the phase values φi and the phase value φ0; and/or determining the rotational direction and/or rotational speed ω from the phase differences Δφi on the basis of a Vernier method.
AMR or GMR sensors (AMR: anisotropic magneto resistance, GMR: giant magneto resistance) may be used as sensors. The sensors each generate a sine signal and a cosine signal, from which the angle to be measured may be calculated in the further processing. Further sensors of the species are, for example, Hall sensors, as well as optical or micromechanical transducers.
Sine signals (y) and cosine signals (x), which may be assigned to the rotational direction and/or rotational speed of the rotatable body, may originate from a single sensor or from multiple sensors. If only one sensor is used, it delivers one sine signal and one cosine signal which is assignable to the rotational direction and/or rotational speed of the rotatable body. If multiple sensors are used, one sensor may output a sine signal which is assignable to the rotational direction and/or rotational speed of the rotatable body, and another sensor may output a corresponding cosine signal.
The sensor signals may be continuous signals and/or discrete signals.
Using suitable methods, in particular the method described in Bosch R. 319810 for efficient offset compensation in angle or phase signals, sine signals (y) and cosine signals (x) output by a sensor may be freed from any signal offsets. This compensation method is described briefly hereafter:
An angle α of angle sensors may be determined on the basis of a sine signal which is assignable to the angle and a cosine signal which is assignable to the angle using the following steps: recording a first value pair S0, having a first sine signal (y0) and a first cosine signal (x0); recording a second value pair S, having a second sine signal (y) and a second cosine signal (x); calculating a third value pair S′ from the difference between second value pair S and first value pair S0; and/or determining angle α on the basis of third value pair S′.
Through the determination of angle α on the basis of the difference between the first and second value pairs, the offsets of the recorded cosine signals or sine signals neither have to be determined nor also taken into consideration.
On the basis of the offset compensation described above or the calculated phase difference Δφi, it is possible to determine the rotational direction and the rotational speed of the rotatable body without knowing the signal offsets.
In a further embodiment according to the present invention, phase values φ may be ascertained from the sine signal (y) and cosine signal (x) with the aid of a CORDIC method (COordinate Rotation Digital Computer) or a series expansion.
In a further embodiment according to the present invention, the points in time ti=t0+n·Δt with n, ΔtεN. n is referred to as the period number and Δt as the granularity.
Period number n may be between 5-50, which may between 10-35, and which may between 15-20. Period number n may be adapted to the type of the sensor. The higher the period number, the greater the precision of the method.
Granularity Δt may be in the range from 1-50 ms, which may be between 5-30 ms, and which may be between 10-15 ms. Granularity Δt may be adapted to the type of the sensor. The selection of the granularity results in the uniqueness range of the rotational frequency determination. At a granularity Δt=10 ms, a uniqueness range of ±50 Hz results, which corresponds to a speed range of ±300 km/h. In particular, the granularity or the sampling times may be selected so that both motion detection and also rotational direction recognition are possible.
According to a further implementation of the exemplary embodiments and/or exemplary methods of the present invention, the phase differences Δφi correspond to the following expression: Δφi=ω·ti mod 2π, ω corresponding to the rotational direction and/or rotational speed and ti to the point in time of the measurement.
According to the exemplary embodiments and/or exemplary methods of the present invention, rotational direction and/or rotational speed ω may be determined from phase differences Δφi on the basis of a Vernier method. The Vernier method may be a multidimensional Vernier method, a classical Vernier method, a modified Vernier method, or a cascaded, modified Vernier method, as described, for example, in DE 101 42 449 A1 of the applicant.
The use of a multidimensional Vernier method has the following advantages: the robustness of the analysis system is very high. The circuit implementation may be designed extremely efficiently in regard to circuit outlay, computing outlay, and power consumption in relation to conventional approaches. No information is required about signal offsets and rotational frequency. No memory capability must be provided for offsets in the sensor system. The offsets do not have to be ascertained in a separate step at the end of tape or in operation, if, for example, the method described above for efficient offset compensation in angle or phase signals is used.
In the meaning of the exemplary embodiments and/or exemplary methods of the present invention, the rotatable body may be a wheel or a shaft.
The method according to the present invention and the device according to the present invention are suitable in particular for analyzing acceleration sensors (micromechanical or piezoelectric) in tire pressure monitoring systems (TPMS), motion detection, and/or auto-location.
In the device according to the present invention, further circuit parts may be combined in a multiplexing method in various embodiments. It is also possible to construct the device as analog, digital, or from a mixture of analog technology and digital technology.
The present invention is explained in greater detail hereafter as an example on the basis of the appended drawings.